A South Carolina death row prisoner chose Friday to die by firing squad instead of an electric chair, after he was required by a new law to pick or the state would choose for him—but he questioned the constitutionality of either punishment.

Richard Moore, 57, wrote in a court filing he more strongly opposes electrocution, but stressed he believes he was forced “to choose between two unconstitutional methods of execution.”

After a decade-long pause in executions in South Carolina due to legal problems with lethal injections, a law that went into effect last year makes electrocution the default, but also allows three volunteer prison workers to shoot rifles toward the inmate’s heart in the case a prisoner chooses the firing squad.

Moore has been on death row for two decades after he was convicted of murder in 2001 for killing a convenience store clerk during an attempted robbery—though Moore claims he acted in self-defense.

Moore, who was unarmed when he entered the store, got into a fight with the clerk, who pulled out a pistol, which Moore wrestled from him.